Constructors and Destructors

Constructor

class integer 

{ int m,n; 

   public : <no data type> integer (void)

        { m = 0 ; n = 0; } };

integer int1;

Characteristics of Constructors

Parameterized Constructors

Multiple Constructors in a Class

integer() {m=0;n=0;}

integer(int x, int y) { m = x; n = y; }

integer(integer & i) { m = i.m; n = i.n }

integer i1;

integer i2;

integer i3(i2);

Constructors With Default Arguments

Dynamic Initialization of Objects

public :

    fixed_deposit() {}

    fixed_deposit(long p, int y, float R = 0.12);

    fixed_deposit(long p, int y, int r);

main() 

{fixed_deposit FD1,FD2,FD3;

// defining and reading p, y, R and r here

FD1 = fixed_deposit(p,y,R); //parameter value 

FD2 = fixed_deposit(p,y);  // provided at run time

FD3 = fixed_deposit(p,y,r);

// displaying them here

Copy Constructor

Assignments and Initializations

Dynamic Constructors

class string 

 { char *name; 

     int length;

  public : 

     string() {length = 0; 

                    name=new char[length +1]; }

     string(char *s)

                 {length = strlen(s); 

                   name=new char[length +1];

                   strcpy(name,s);}

void join(string & a, string & b)

   { length = a.length + b.length;

      delete name; name = new char[length+1];

      strcpy(name,a.name); 

      strcat(name,b.name); }

char *first=“This”; //In the main()

string name1(first),name2(“is”),name3(“testing”);

string s1,s2;

s1.join(name1,name2);

s2.join(s1,name3);

s2.display();

Constructing Two Dim Arrays

class matrix

{ int **p; int d1,d2;

  public :

     matrix(int x, int y)

      { d1 =x; d2 =y ; p = new int *[d1];

         for (int i = 0 ; i < d1; ++i)

                    p[i] = new int[d2];  }

     void get_element(int i,int j,int value)

       { p[i][j] = value}

     int & put_element(int i, int j)

       { return p[i][j] }                           

}

Destructors

matrix ::~matrix()

 { for (int i = 0; i< d1; i++) delete p[i];

     delete p; }